90° power divider

ABSTRACT

The invention relates to a 90° power divider for distributing the power of an input signal (E) to two output branches (A 1 , A 2 ) that are phase-shifted against each other by 90°. A capacity (C) is arranged in one output branch (A 1 ) and an inductivity (L) is arranged in the remaining output branch (A 2 ). Said capacity and inductivity are measured as follows: C=½*π*Z 1 *Fo, L=Z 2 /2*π*Fo, whereby Fo is the centre frequency and Z 1  and Z 2  are the terminating resistances of the output branches (A 1 , A 2 ) respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a 90° power divider.

2. Description of the Prior Art

Power dividers of this kind are known. They have been produced to datein the form of directional couplers, hybrid coupler or similar couplercircuits, for example with transformers. These known power dividers arecomplicated and expensive.

SUMMARY

It is the object of the invention to create a 90° power divider, whichcan be produced very simply and cheaply.

This object is achieved based on a 90° power divider according to thepreamble of the main claim by its characterising features. Advantageousfurther developments emerge from the subordinate claims.

A 90° power divider according to the invention can be produced verysimply by means of a capacitor and a coil and it additionally has theadvantage that it can be very highly driven, which is important inparticular in its application in radio transmitters. It has furtherproved particularly advantageous to use a 90° power divider of this kindwith an I/Q modulator, I/Q demodulator or a quadrature mixer forgenerating the two I and Q components phase-shifted against each otherby 90°. It can equally well be used for in-phase adding.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the basic circuit diagram of a 90° power divider accordingto the invention, consisting of a capacitor C and an inductivity L.

FIG. 2 shows a basic circuit diagram of an I/Q modulator of anembodiment of the invention in which the carrier as input signal isdivided via a capacitor C and an inductivity L into carrier signalsphase-shifted against each other by 90°, which are then supplied viaamplifiers V1 or V2 to the mixers M1 or M2 of the I/Q modulator, inwhich they are multiplied by the I and Q components.

FIG. 3 shows a 90° power divider according to the invention that issuitable for connecting two amplifier stages in parallel in order toincrease the achievable output power.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is described in greater detail below by embodimentexamples using schematic drawings.

FIG. 1 shows the basic circuit diagram of a 90° power divider accordingto the invention, consisting of a capacitor C and an inductivity L. Atthe input E an input signal is supplied which is to be distributed tothe two output branches A1 and A2, which are terminated in each case bya load Z1 or Z2. For distributing the power of the input signal E inequal parts, to the two loads Z1 and Z2 with a mutual phase shift of 90°the following relation applies to the dimensioning of the capacitor Cand the inductivity L: $C = \frac{1}{2*\pi*Z_{1}*{Fo}}$$L = \frac{Z_{2}}{2*\pi*{Fo}}$

Fo is therein the operating frequency. Advantageously the two loadresistances Z1 and Z2 are chosen as of equal size, corresponding to thesystem impedance preferably 50 ohms. In this way it is achieved thatpower adaptation also prevails at the input E.

By means of the arrangement according to the invention it is achievedthat the capacitive branch is leading by +45° and the inductive branchis lagging by −45°. From this emerges a differential phase of 90°between port 2 and port 3. This differential phase is maintained over awide frequency range. If the frequency range diverges too far from thecentre frequency Fo, the power is no longer distributed in equal parts.With increasing frequency the capacitive branch takes up more power andwith falling frequency the inductive branch takes up more power. If adifference of 1 dB is allowed between A1 and A2 as a permissibledifference in power, the arrangement can be operated over a bandwidth ofapproximately 28%. The relation between the centre frequency and thefrequency limits is as follows:

For Fo: Fo={square root over (Fmin*Fmax)}applies.

Since C and L represent complementary elements, the input impedances ofthe two load branches compensate one another in that the parallelcircuit of the two branches again makes the charge impedance Z appear atthe input. This ensures good adaptation at the input.

The power divider according to the invention is eminently suitable forthe construction of I/Q modulators, I/Q demodulators or so-calledquadrature mixers, as in this way expenditure on circuits of this kindis considerably reduced compared with conventional solutions and thepower dividers can additionally be very highly driven. In this way I/Qmodulators can be constructed which, for example, can be directly loopedinto the signal branch of a transmitter processing. The highsignal-to-noise ratio needed for many high frequency transmitters cantherefore usually be achieved without problems. FIG. 2 shows the basiccircuit diagram of an I/Q modulator of this kind, in which the carrieras input signal is again divided via a capacitor C and an inductivity Linto carrier signals phase-shifted against each other by 90°, which arethen supplied via amplifiers V1 or V2 to the mixers M1 or M2 of the I/Qmodulator, in which they are multiplied by the I and Q components. Thethus generated output signals are then combined in an adder D into asingle output signal, which is then further processed. The additionalamplifiers V1 and V2 increase the level before the mixers M1 and M2,which improves the signal-to-noise ratio of the output signal. At thesame time these amplifiers represent a load, independent of modulation,for the power divider, as they decouple the input impedance which inmany mixers is dependent on drive.

The I and Q components can also, of course, be generated by a 90° powerdivider according to the invention in the same way.

A 90° power divider according to the invention is also very suitable forconnecting two amplifier stages in parallel, in order to increase theachievable output power, as shown in FIG. 3. For this purpose in each ofthe two branches A1 and A2 after the power divider L, C an amplifier V1,V2 is arranged in each case and the output signals of these twoamplifiers V1 and V2 are combined with a further circuit consisting ofan inductivity L and a capacitor C, which corresponds to the 90° powerdivider on the input side. The inductivity L and the capacitor C on theoutput side are, however, constructed to mirror the arrangement of thepower divider at the input, so the desired in-phase summation isachieved at the output. This circuit for increasing power isparticularly suitable for connecting together so-called MMICs, as theseare normally adapted internally to 50 ohms and thus suit this kind ofpower divider. If the drop in power at the limits of the usablebandwidth and certain losses are taken into account, with an arrangementof this kind a drive 2 dB higher than with a single amplifier can beachieved.

What is claimed is:
 1. 90° power divider for distributing the power ofan input signal (E) to two output branches (A1, A2) phase-shiftedagainst each other by 90°, characterised in that in one output branch(A1) a capacity C and in the other output branch (A2) an inductivity Lis arranged, with dimensions as follows:$C = \frac{1}{2*\pi*Z_{1}*{Fo}}$ $L = \frac{Z_{2}}{2*\pi*{Fo}}$

wherein Fo is the centre frequency and Z1 and Z2 are in each case theterminating resistances of the output branches (A1, A2).
 2. 90° powerdivider according to claim 1, characterised in that the two outputbranches (A1, A2) are terminated in each case with the same impedance(Z).
 3. 90° power divider according to claim 1 or 2, characterised byits application in an I/Q modulator, I/Q demodulator or a quadraturemixer.
 4. 90° power divider according to claim 1 or 2, characterised byits application for parallel connection on the input and output side oftwo individual amplifier stages (V1, V2), wherein the capacitors C andinductivities L are connected at the input or output in each case asmirrored to one another.
 5. 90° power divider for distributing the powerof an input signal (E) to two output branches (A1, A2) phase-shiftedagainst each other by 90°, characterised in that in one output branch(A1) a capacity C and in the other output branch (A2) an inductivity Lis arranged, with dimensions as follows:$C = \frac{1}{2*\pi*Z_{1}*{Fo}}$ $L = \frac{Z_{2}}{2*\pi*{Fo}}$

and further characterised in that in the two output branches (A1, A2) ineach case an amplifier (V1, V2) is arranged in series to the capacitor Cor the inductivity L, wherein Fo is the centre frequency and Z1 and Z2are in each case the terminating resistances of the output branches (A1,A2).
 6. 90° power,divider according to claim 5, further characterised inthat the two output branches (A1, A2) are terminated in each case withthe same impedance (Z).
 7. 90° power divider according to claim 5 or 6,further characterised by its application in an I/Q modulator, I/Qdemodulator or a quadrature mixer.